Gear pump with trapping reliefs



Dec. 10, 1963 J. J. FULTON 3,113,524

GEAR PUMP WITH TRAPPING RELIEFS Filed Dec. 26, 1961 2 Sheets-Sheet 1 rmwin find 5am WWW WW1; +01% United States Patent Oflfice Patented Dec.10, 1963 3,113,524 GEAR hUMP WITH TRAPPING RELEFS John .1. Fulton,Rockford, EL, assignor to Roper Hydraulics, Ina, Commerce, Ga, acorporation of Georgia Filed Dec. 26, 1961, Ser. No. 162,124 6 Claims.(Ql. 163-12) This invention relates to fluid pump and particularly to agear-type pump having trapping-relief grooves.

In pumps having intermeshing gears, problems are encountered due toentrapment of liquid in the intertooth spaces as the gear teeth moveinto meshing engagement, and trapping reliefs have heretofore beenprovided at the discharge side of the gear mesh for relieving thetrapped liquid to the pump outlet. Problems are also encountered incompletely filling the toothed spaces in such pumps as the gears moveout of meshing engagement and inlet grooves have heretofore beenprovided in the end walls of the pump chambers for feeding liquid fromthe pump inlet along the ends of the gear teeth to the tooth spaces toassist in filling the same. However, the relatively low pressure at thepump inlet limits the rate at which the inlet fluid will flow into thetooth spaces and this has heretofore limited the maximum speed at whichthe pump could be driven, while still achieving complete filling of thetooth spaces.

An important object of this invention is to provide a pump having animproved arrangement for filling the tooth spaces at the inlet side ofthe pump to enable complete filling of the tooth spaces at higher pumpspeeds than can be achieved when the fluid at only pump inlet pressureis fed into the gear teeth.

Another object of this invention is to provide a gear pump having animproved arrangement for relieving the fluid trapped in the tooth spacesas the gear teeth move into meshing engagement, and for filling thetooth spaces at the inlet side of the pump as the gear teeth move out ofmeshing engagement.

A more particular object of this invention is to provide a gear pumphaving trapping relief recesses at the inlet side of the pump arrangedto direct trapped fluid back into the tooth spaces as the gears move outof meshing engagement at the inlet side of the pump, to thereby have thetrapped fluid assist in filling the tooth spaces.

Yet another object of this invention is to provide a pump in accordancewith the foregoing objects and in which the trapped fluid is directedinto the tooth spaces at the inlet side of the pump in such a mannerthat the trapped fluid does not oppose the normal flow of fluid from thepump inlet to the gear teeth.

These, together with various ancillary objects and advantages of thisinvention will be more readily appreci ated as the same becomes betterunderstood by reference to the following detailed description when takenin connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view through a pump embodying thetrapping relief grooves of the present invention;

PEG. 2 is a transverse sectional view through the pump, taken on theplane 22 of FIG. 1;

FIGS. 3 and 4 are fragmentary sectional views illustrating the meshpoint of the gears, with the gears in different positions;

FIG. 5 is a fragmentary sectional view taken on the plane 55 of FIG. 3;and

FIG. 6 is a fragmentary sectional view taken on the broken section line6-6 of FIG. 3.

The present invention relates particularly to rotary gear pumps and, asshown herein, the pump includes a pump casing having a body 1% formedwith intersecting bores 11 and 12 and end walls 13 and 14 secured toopposite ends of the body. The end walls are conveniently detachablysecured to the body as by bolts 15 which extend between the end Walls,and seals such as the 0 rings 16 are provided for sealing the interfacebetween the end walls and the body. A pair of meshing gears 21 and 22are disposed in the pump bores 11 and 12 respectively and have axiallyextending trunnions or axles 23 and 24. The gears may be formedintegrally With the trunnions or, can be formed separately therefrom andnon-rotatably connected to the trunnions by suitable keys or splines.

End plates are provided at opposite ends of the pump gears 21 and 22 inclose running fit with the end faces of the gears. The end plates arepreferably supported in the pump bores and the end plates at one or bothends of the gears are slidable in the bores to maintain a close runningfit with the end faces of the gears. In order to facilitate machining ofthe end plates, the end plates are preferably in the form of twoseparate bushings designated 25 and 26 each having a generally circularperipheral portion 27 which are slidably received in the respectivebores 11 and 12 and a flat chordal portion designated 29, as best shownin FIG. 2. The chordal portions 29 etend tangent to the pitch circles ofboth gears at the mesh point thereof and abut each other at theintersection of the pump bores. The gear trunnions 23 and 24 arerotatably supported in bearings 32 and 33 and which bearings areconveniently mounted in the bushings 25 and 26 respectively. Theinterface between the bushings 25 and 26 and the respective pump bores11 and 12 is sealed by a generally figure 8 shaped gasket 35 which isdisposed in a groove 36 in the periphery of the circular portions 27 and28 of the bushings. As best shown in FIGS. 1 and 5, the gasket ispreferably formed with a channel shaped cross section and meansdescribed hereinafter is provided for maintaining the passage 36 underpressure to press the gasket outwardly into sealing engagement withthe'pump bores.

' One of the gears such as the gear 21 is the drive gear and one of thejournals 23 on the drive gear has an extension 4-1 which extends out ofthe pump housing through a shaft seal 42 and is adapted for connectionat 43 to a pump drive mechanism (not shown). The pump is'provided withan inlet opening 45 and a discharge opening 46 at opposite sides of thegear mesh and the drive gear 21 is rotated in a direction(counterclockwise) as viewed in FIG. 2 to pump fluid from the inlet 45to the outlet 46. As the gears are rotated, fluid is carried in thespaces between the teeth 51 and 52 on the drive and driven gears 21 and22 respectively from the inlet 45 to the outlet 46. As the gear teethmove into meshing engagement, the lead faces 51a of the teeth on thedrive gear 21 engage the trailing faces 52b of the teeth on the drivengear 22. This seals off the intertooth spaces 51c and 52c in the driveand driven gears from the inlet and outlet. The fluid remaining in thespaces is thus trapped and, as the teeth move from the outlet sidetoward the plane through the axis of the gears, the trapped volume ofthe intertooth spaces decreases and, conversely, as the teeth move awayfrom the plane through the axis of the gears toward the inlet side, thetrapped volume of these intertooth spaces increases. As a practicalmatter, it is necessary to provide some backlash between the gears and,preferably, the gears are formed with more backlash than is normalpractice so that the trailing face 51b of the teeth on the drive gear isspaced slightly from the lead face 52b of the teeth on the drive gear tointercommunicate the tooth spaces 51c in the drive gear with the toothspaces 520 in the driven gear at the gear mesh. In order to relieve theexcessive pressures which are otherwise developed in the intertoothspaces as they decrease in volume at the outlet side of the pump, it isthe usual practice to provide trapping relief recesses at the outsideor" the pump. It is also customary to provide inlet recesses at theinlet side of the pump for feeding fluid from the inlet along the endsof the gear teeth to the intertooth spaces as they increase in volume atthe inlet side of the pump.

The pressure at the inlet of the pump is usually relatively low andthere is a limit to the rate at which the fluid can flow under this lowinlet pressure along the ends of the gear teeth and into the intertoothspaces to completely fill the same. This limits the maximum speed atwhich the pump can be operated with complete filling of the gear teeth.In accordance with the present invention, an improved trapping reliefarrangement is provided which utilizes some of the trapped fluid to aidin filling the intertooth spaces at the inlet side of the pump, and insuch a manner as to not interfere with the normal filling of the toothspaces by the fluid entering the same from the pump inlet. As best shownin FIGS. 2-4, outlet trappin-g relief recesses 61 and inlet sidetrapping relief recesses 62 are provided in the end plates or bushingsat at least one end of the pump gears, and preferably in the end platesor bushings at both ends of the pump gears. The outlet and inlettrapping relief recesses are spaced apart a distance suflicient toprevent open communication through the intertooth spaces in allpositions of the pump gears and, preferably, the inner side edges 61aand 62a of the outlet and inlet relief recesses are angularly spacedapart a distance such that, when the leading edge 51a of the tooth onone gear such as the drive gear begins to cover the outlet recess 61,the trailing edge such as 52b of the preceding tooth on the other gearbegins to uncover the other recess 62. Thus, as shown in FIG. 2, theleading edge 51a of one tooth on the drive gear 21 is approaching aposition which cuts off communication with the tooth space 51c and theoutlet trapping relief recess 61, while the trailing edge 52!; on thenext preceding tooth of the driven gear is approaching a position inwhich it will communicate the tooth space 520 with the inlet trappingrelief recess 62. This angular spacing between the adjacent edges of theinlet and outlet trapping relief recesses is generally slightly lessthan the angular distance between corresponding teeth on the gear and,for the ten tooth gears shown, in which the spacing between the leadedges of the adjacent teeth is 36, the angular spacing between theadjacent edges 51a and 62a of the outlet and inlet relief recesses isabout 33. With this arrangement, the trapped spaces 51c and 520 will berelieved to the outlet relief recess 61 until the lead edge of the toothon the drive gear moves across the edge 61a of the outlet relief recess.At about that time, the trailing edge of the preceding tooth on thedriven gear 22 will uncover the inlet relief recess 62, as shown in FIG.3, to relieve the trapped fluid to the inlet relief recess. The trappedfluid relieved to the inlet of the pump would normally be in a directionto oppose the flow of fluid from the pump inlet into the intertoothspaces so that it would not only reduce the pump efficiency but wouldalso oppose proper filling of the tooth spaces with fluid. In accordancewith the present invention, the inlet trapping relief recesses areshaped so as to deflect the trapped fluid back into the intertoothspaces at the inlet side of the pump to aid in filling the tooth spaces,and in a direction such that relieved fluid does not oppose the normalflow of fluid from the pump inlet into the tooth spaces. As best shownin FIG. 5, the inlet trapping relief recesses 62 are formed with asmoothly Iarcuate and preferably semi-cylindrical base wall whichextends fromthe inlet edge 62a to the outlet edge 62b of the recess.Thus, trapped fluid which is discharged from the tooth spaces such as520 into the inlet relief recesses 62 is deflected back into theintertooth spaces to aid in filling the same. As the fluid enters theintertooth spaces from the relief recesses, it is flowing in a directiongenerally normal to the direction of flow from the pump inlet to thegear teeth, and therefore does not oppose filling of the tooth spacesfrom the pump inlet. While the flow of trapped fluid through the reliefrecess 62 will vary in direction and magnitude as the gear teeth movepast the relief recess, a typical flow passage for the relieved fluid isshown by arrows in FIG. 6 and designated by the letter R. As will beseen from a comparison of FIGS. 3 and 6, fluid in closing trapped space510 in the drive gear passes through the backlash between the trailingface of one tooth on the drive gear and the lead edge of one tooth onthe driven gear into the tooth space 52c, and is relieved through theinlet relief recess 62 into the tooth space 510 of the drive gear.

In order to properly direct the fluid into the tooth spaces at the inletside of the gears, it is necessary that the inlet relief recesses 62 canbe spaced inwardly of the addendum circle of the gears. The outer edge62b of the inlet relief recesses thus intersect the chordal surfaces 29at a point inwardly of the inlet edge thereof. These chordal surfacesare preferably disposed in a plane which is tangent to the pitch circlesof both gears, and which plane thus extends perpendicular to a planethrough the gear axes. For best performance, the inner edge of therecesses 62 is inclined to the tangent plane previously described so asto extend generally parallel to the edge of the tooth :base as the toothmoves thereacross. The portions of the inlet relief recess in each ofthe bushings are preferably similarly shaped and produce an overallchevron-shaped recess. These recesses with the arcuate base Walls canconveniently be formed by simple milling operation and extend inwardlyto the root diameter of the teeth. At that point, they terminate in anabrupt semicircular end wall 62c, clearly shown in FIG. 5.

The trapping relief recesses 61 at the outlet side of the pump canconveniently be formed in the same manner and with the same shape as theinlet relief recesses previously described and, as shown, have an outeredge 61b which extends generally parallel to the inner edge 61a thereofand have an arcuate base Wall that extends between the inner and outeredges to deflect the trapped liquid into the outlet. Alternatively, theoutlet tnapping relief recesses could extend all the way to theperiphery of the bushings, if desired.

The outlet trapping relief recesses are advantageously communicatedthrough a lateral passage 71 formed on. the chordal surfaces 29 of thebearing bushings with the gasket recess 36 in the bushings, to supplyfluid at discharge pressure to the underside of the gasket 35. Aspreviously described, this pressurizes the gasket outwardly against thewalls of the pump bore to maintain a seal around the bushings.

The difference in pressure between the .pump outlet and pump inlet,acting on the gear peripheries, produces a radial hydraulic thrust in adirection generally toward the pump inlet. As is common practice,pressure angle adjusting grooves 72 are conveniently formed in the endfaces of the bushings adjacent the roots of the teeth and extend fromthe outlet side of the pump and part way around the bushing andterminate short of the inlet, to distribute outlet pressure over asubstantial portion of the gear peripheries.

From the foregoing, it is thought that the operation and construction ofthe device will be readily understood and further detailed descriptionis deemed unnecessary. As will be noted, the fluid trapped in theintertooth spaces is alternately discharged through the outlet reliefrecesses 61 and the inlet relief recesses 62. The latter are shaped insuch a manner to deflect the trapped fluid back into the tooth spaces atthe inlet side of the pump to aid in filling the tooth spaces and insuch a manner as to not oppose the normal filling of the tooth spacesfrom the pump inlet. This trapped fluid which is discharged back intothe opening tooth spaces at the pump inlet is at substantially higherpressure than the fluid at the pump inlet and markedly aids in fillingthe tooth spaces so that the pump can be operated at substantiallyhigher speeds than could otherwise be achieved, While still maintainingcomplete filling of the tooth spaces. This increases the overall pumpefliciency and reduces cavitation and noise.

I claim:

1. A gear pump comprising, a pump casing having a pair of intersectingbores and end plates at opposite ends of said bores defining a pumpchamber, a pair of meshing rotary gears in said pump bores having theends thereof in running engagement with the faces of said end plates andincluding a drive gear and a driven gear, means in said casing providingan inlet on one side of the gear mesh and an outlet at the other side ofthe gear mesh, at least one of said end plates having a trapping reliefrecess at the inlet side of the pump disposed entirely within theaddendum circle of the driven gear, said trapping relief recess havingan inner side edge extending transverse to a common plane tangent to thepitch circles of both gears and intersecting said tangent plane at apoint spaced from a plane through the gear axes toward the inlet side ofthe pump, said inner side edge of said recess extending to a pointadjacent the root diameter of the driven gear and being angularly spacedfrom said plane through the gear axes a distance slightly less than onehalf the pitch of the teeth on the driven gear, said relief recesshaving an outer side edge intersecting said tangent plane at a pointrelatively farther from the said plane through the gear axes and spaceda substantial distance inwardly of the addendum circle of the gears,said recess having a curved base wall curving from said inner edge intothe end plate and then back to said outer edge and extendingsubstantially normal to the face of the end plate at said outer edge ofthe recess to direct the trapped liquid back into the tooth spaces atthe inlet side of the pump in a direction substantially normal to thedirection of fluid flow from the pump inlet to the gears to aid infilling the tooth spaces.

2. The combination of claim 1 wherein said inner and outer edges of therecess are inclined to said tangent plane to extend generally radiallyof said drive gear.

3. A gear pump comprising, a pump casing having a pair of intersectingpump bores and end plates at opposite ends of said bores defining a pumpchamber, a pair of meshing rotary gears in said pump bores having theends thereof in running engagement with thefaces of said end platesincluding a drive gear and a driven gear, means in said casing providingan inlet on one side of the gear mesh and an outlet at the other side ofthe gear mesh, at least one end plate comprising a pair of bushingshaving an outer diameter substantially equal to the addendum circle ofthe gears and slidably mounted in said bores to maintain the facethereof in close running fit with the end of the gears, said pair ofbushings having flat chordal sur faces abutting each other at a commonplane tangent to the pitch circles of both gears, said bushings eachhaving an outlet trapping relief recess in the face thereof at theoutlet side of the gear mesh, said bushings each having an inlettrapping relief recess in the face thereof at the inlet side of the gearmesh disposed entirely within the addendum circles of the gears andspaced inwardly of the Outer periphery of the respective bushing, saidinlet and outlet relief recesses in each bushing each having an innerside edge extending transverse to the respective chordal surface andintersecting the latter at a point spaced from a plane through the gearaxes toward the inlet side of the pump, the inner side edges of theinlet and outlet relief recesses in each bushing extending to a pointadjacent the root diameter of the respective gear and being angularlyspaced apart a distance slightly less than the pitch of the gear teethto define a sealing land therebetween, said inlet relief recesses eachhaving an outer side edge extending transverse to the respective chordalsurface and intersecting the latter at a point relatively farther fromthe plane through the gear axes and spaced a substantial distanceinwardly of the end of said chordal surface, said inlet relief recess ineach bushing having a curved base wall curving from the inlet edge intothe bushing and then back to the outlet edge and extending substantiallynormal to the face of the bushing at said outer edge to deflect thetrapped liquid back into the tooth spaced at the inlet and in adirection transverse to the direction of fiow of liquid from the pumpinlet to the gear teeth to aid in filling the gear teeth.

4. The combination of claim 3 wherein said inner edge of the inletrelief recess in each bushing is inclined to said chordal surface toextend generally radially of the respective bushing whereby the inletrelief recesses diverge relative to each other in a direction away fromthe inlet.

5. A gear pump comprising, a pump casing having a pair of intersectingpump bores and end plates at opposite ends of said bores defining a pumpchamber, a pair of meshing rotary gears in said pump bores having theends thereof in running engagement with the faces of said end platesincluding a drive gear and a driven gear, means in said casing providingan inlet on one side of the gear mesh and an outlet at the other side ofthe gear mesh, at least one end plate comprising a pair of bushingshaving an outer diameter substantially equal to the addendum circle ofthe gears and slidably mounted in said bores to maintain the facethereof in close running fit with the end of the gears, said pair ofbushings having flat chordal surfaces abutting each other at a commonplane tangent to the pitch circles of both gears, said bushings eachhaving an outlet trapping relief recess in the face thereof at theoutlet side of the gear mesh, said bushings each having an inlettrapping relief recess in the face thereof at the inlet side of the gearmesh disposed entirely within the addendum circles of the gears andspaced inwardly of the outer periphery of the respective bushing, saidinlet and outlet relief recesses in each bushing each having an innerside edge extending transverse to the respective chordal surface andintersecting the latter at a point spaced from a plane through the gearaxes toward the inlet side of the pump, the inner side edges of theinlet and outlet relief recesses in each bushing extending to a pointadjacent the root diameter of the respective gear and being angularlySpaced apart a distance slightly less than the pitch of the gear teethto define a sealing land therebetween, said inlet relief recesses eachhaving an outer side edge extending transverse to the respective chordalsurface and intersecting the latter at a point relatively farther fromthe plane through the gear axes and spaced a substantial distance in-War-dly of the end of said chordal surface, said inlet relief recess ineach bushing having a generally semi-cylindrical configuration with theaxis of each semi-cylindrical recess generally paralleling the face ofthe respective bushing, the axes of the inlet relief recess in bothbushings be ing inclined to the chordal surface to extend generallyradially of the respective bushing.

6. A gear pump comprising, a pump casing having a pair of intersectingpump bores and end plates at opposite ends of said bores defining a pumpchamber, a pair of meshing rotary gears in said pump bores having theends thereof in running engagement with the faces of said end platesincluding a drive gear and a driven gear, means in said casing providingan inlet on one side of the gear mesh and an outlet at the other side ofthe gear mesh, at least one end plate comprising a pair of bushingshaving an outer diameter substantially equal to the addendum circle ofthe gears and slidably mounted in said bores to maintain the facethereof in close running fit with the end of the gears, said pair ofbushings having flat chordal surfaces abutting each other at a commonplane tangent to the pitch circles of both gears, said bushings eachhaving an outlet trapping relief recess in the face thereof at theoutlet side of the gear mesh, said bushings each having an inlettrapping relief recess in the face thereof at the inlet side of the gearmesh disposed entirely within the addendum circles of the gears andspaced inwardly of the outer periphery of the respective bushing, saidinlet and outlet relief recesses in each bushing each having an innerside edge extending transverse to the respective chordal surface andintersecting the latter at a point spaced from a plane through the gearaxes toward the inlet side of the pump, the inner side edges of theinlet and outlet relief recesses in each bushing extending to a pointadjacent the root diameter of the respective gear and being angularlyspaced apart a distance slightly less than the pitch of the gear teethto define a sealing land therebetween, said inlet relief recesses eachhaving an outer side edge extending transverse to the respective chordalsurface and intersecting the latter at a point relatively farther thanthe plane through the gear axes and spaced a substantial distanceinwardly of the end of said chordal surface, said inlet and outletrelief recesses in each bushing having a generally semi-cylindricalconfiguration with the axis of each semi-cylindrical recess generallyparalleling the face of the respective bushing, the axes of each reliefrecess being inclined to the chordal surface to extend generallyradially of the respective bushing.

References Cited in the file of this patent UNITED STATES PATENTS1,129,091 Hawley Feb. 23, 1915 1,659,771 Fox Feb. 21, 1928 1,719,025Scherninger July 2, 1929 2,833,224 Meyer et al May 6-, 1958 2,870,720Lorenz Jan. 27, 1959 2,884,864 Bobnar May 5, 1959 2,990,783 Oliver July4, 19 61

1. A GEAR PUMP COMPRISING, A PUMP CASING HAVING A PAIR OF INTERSECTINGBORES AND END PLATES AT OPPOSITE ENDS OF SAID BORES DEFINING A PUMPCHAMBER, A PAIR OF MESHING ROTARY GEARS IN SAID PUMP BORES HAVING THEENDS THEREOF IN RUNNING ENGAGEMENT WITH THE FACES OF SAID END PLATES ANDINCLUDING A DRIVE GEAR AND A DRIVEN GEAR, MEANS IN SAID CASING PROVIDINGAN INLET ON ONE SIDE OF THE GEAR MESH AND AN OUTLET AT THE OTHER SIDE OFTHE GEAR MESH, AT LEAST ONE OF SAID END PLATES HAVING A TRAPPING RELIEFRECESS AT THE INLET SIDE OF THE PUMP DISPOSED ENTIRELY WITHIN THEADDENDUM CIRCLE OF THE DRIVEN GEAR, SAID TRAPPING RELIEF RECESS HAVINGAN INNER SIDE EDGE EXTENDING TRANSVERSE TO A COMMON PLANE TANGENT TO THEPITCH CIRCLES OF BOTH GEARS AND INTERSECTING SAID TANGENT PLANE AT APOINT SPACED FROM A PLANE THROUGH THE GEAR AXES TOWARD THE INLET SIDE OFTHE PUMP, SAID INNER SIDE EDGE OF SAID RECESS EXTENDING TO A POINTADJACENT THE ROOT DIAMETER OF THE DRIVEN GEAR AND BEING ANGULARLY SPACEDFROM SAID PLANE THROUGH THE GEAR AXES A DISTANCE SLIGHTLY LESS THAN ONE